Aircraft applicable circuit imbalance detection and circuit interrupter and packaging thereof

ABSTRACT

The aircraft applicable current imbalance detection and circuit interrupter interrupts an electrical circuit when a current imbalance is sensed. The current imbalance detection and circuit interrupter includes a housing, power supplies, a sensor system for sensing a current imbalance at the line side of the electrical circuit, a logic controller and a power controller including a power relay having contacts capable of surviving carry-break and make-carry-break types of ground fault conditions at anticipated current levels. At power up, the device performs a test to confirm that none of the relay contacts have failed in a closed position, and to check whether a switching FET which controls the relay coil has shorted.

RELATED APPLICATIONS

This is a continuation in part of Ser. No. 10/611,218, filed Jul. 1,2003, which is a divisional of Ser. No. 09/954,474, filed Sep. 14, 2001,now U.S. Patent No. 6,618,229, which is a continuation in part of Ser.No. 09/775,337, filed Feb. 1, 2001, now U.S. Pat. No. 6,583,975.

BACKGROUND OF THE INVENTION

This invention relates generally to electrical control systems, and morespecifically to an aircraft electrical control system which disconnectspower to a load when a current imbalance is sensed.

In the electromechanical arts, current imbalances are indicative ofserious problems that can lead to disastrous results, such as arcingwithin fuel pumps. Since fuel pumps are often housed within a fuelvessel to directly pump fuel out of the vessel, arcing within a fuelpump can lead to an explosion of fuel-air mixture and a subsequentbreach of the fuel vessel, which can be catastrophic. In light of theseriousness of such an event, a device or methodology is needed whichcan suppress this type of arcing, as well as other associated problems.Presently, a common type of circuit protection device being utilized inaircraft is a thermal circuit breaker. However, arcing typically doesnot cause thermal circuit breakers to activate. Thus, there has been along-felt need for the function of current imbalance detection in anaircraft. One very important form of current imbalance is a ground faultin which current is flowing between a circuit or electrical device toground, when such current flow is not desired. In the prior art, groundfault detection has been addressed by a separate ground faultinterruption unit. However, such prior art systems have had limitations,including the necessity of rewiring the aircraft. In addition to therequirement to rewire the aircraft, additional space had to be found toaccommodate the ground fault interruption system.

One currently available ground fault interruption unit made by Autronics(model 2326-1) has been used in large commercial aircraft for thepurpose of ground fault protection for fuel pumps. The Autronics unitdetects a ground fault and outputs a signal indicative of a fault by useof a current transformer and acts by removing power to the fuel pumpcontrol relay.

Two different types of ground fault conditions can occur. The first typeof ground fault condition occurs during normal ground fault interruption(GFI) operation (Control Voltage On state), in which the ground faultoccurs after the relay contacts are closed, and power is being providedto the load. In relay terminology, this is known as “carry-break,” i.e.,the relay contacts are fully closed and carrying the current when acontact has to interrupt the fault current. Many conventional 25 Amprelays can interrupt as much as a 500 Amp current without failure.However, the second type of ground fault condition is a more severecondition for relay contacts. This second type of ground fault conditionoccurs when the GFI is just powered and the relay contacts close into anexisting ground fault. In relay terminology, this is known as“make-carry-break,” i.e., the relay contacts have just closed and therelay is immediately commanded to open and interrupt the fault current.In this second type of ground fault condition, severe arcing can occurat the relay contacts as a result of “contact bounce,” in which movingcontacts make and break electrical contact several times due to theirinherent mass and springiness before the contacts come to rest.Unfortunately, severe arcing can occur during contact bounce in thistype of ground fault condition which can also result in the weldingtogether of the relay contacts. Tests performed with relays have shownthat in this second type of ground fault condition, 25 Amp conventionalrelay contacts can become welded together with an arcing ground faultcurrent as low as 150 Amps.

A need therefore exists for an improved circuit protection device foraircraft that can handle both carry-break and make-carry-break types ofground fault conditions, and fault current amplitudes, so as to insurethat ground fault interruption can always be carried out without failureof the ground fault circuit interrupter. It would also be desirable toprovide a ground fault circuit interrupter that at power up will performa test to confirm that none of the relay contacts have failed in aclosed position, and to check that the switching FET which controls therelay coil has not shorted.

It would further be desirable for the circuit protection device to beincluded within an existing device in the aircraft, or to be packagedwith an existing device, sharing the same connections to existingelectrical circuits, since space for avionics is limited in any aircraftand adding wiring to accommodate a new device is very difficult. Thepresent invention addresses these and other concerns.

SUMMARY OF THE INVENTION

Ground fault detection to reduce arcing in aircraft electrical systems,including aircraft fuel pumps, has become a major concern of the FederalAviation Administration, and recent studies have promulgated a varietyof studies and regulations in an attempt to prevent fuel tank ignition.

The present invention is a current imbalance detection and circuitinterrupter particularly attractive for use in aircraft, for protectinga circuit having a line side and a load side. In a currently preferredembodiment, the present invention incorporates the current imbalancedetection and circuit interrupter within the existing aircraft powercontrol relay package. For example, in a fuel system application, thecurrent imbalance detection and circuit interrupter is incorporatedwithin the fuel pump control relay package. Therefore, the invention canbe retrofit to existing aircraft, or can be utilized in newlyconstructed aircraft and new aircraft designs already incorporating therelay system. The current imbalance detection and fault circuitinterrupter includes a housing, a power supply, a circuit to bemonitored, a sensor system, a logic controller, and a power controller(for example: relay, contactor, solid state relay, etc.). In a presentlypreferred embodiment, the invention can also include a fault indicator,a press to test switch and a reset switch. The power supply isconfigured to provide power to the sensor, logic controller and thepower controller. The sensor system is configured to sense a currentimbalance in the circuit being monitored. In one presently preferredembodiment, the sensor system to monitor current imbalance includes aHall effect device, although the sensor system may alternatively includea current transformer (CT) or giant magneto resistive (GMR) device, forexample, or another similar suitable device. The logic controller isconfigured to monitor a relay control input signal and to process inputsfrom the sensor.

In a presently preferred embodiment, the logic controller compares thesensor signal with predetermined limits representing acceptableoperation and outputs a signal representing a circuit current imbalancewhen the sensor signal is outside the acceptable limits. The powercontroller is configured to receive input from the logic controller andremove power to the load side of the circuit when a current imbalance issensed. In a presently preferred embodiment, the power removal from theload side of the circuit due to a sensed current imbalance is maintaineduntil the power source to the current imbalance detection and circuitinterrupter is cycled. In another presently preferred embodiment, powerremoval is maintained until a reset switch is activated. In a presentlypreferred embodiment, the fault indicator provides an indication ofwhether a current imbalance condition has occurred. A press to testswitch may be included to check the operation of the unit duringmaintenance. In a presently preferred embodiment, the fault reset switchis used to reset the fault indicator and the current imbalance detectionand circuit interrupter.

The present invention also provides for a method for interrupting anelectrical circuit for an electrical load, the electrical circuit havinga line side and a load side with a ground fault. In summary, the methodcomprises providing a supply of power, continually monitoring andsensing the circuit for a current imbalance, continually monitoring therelay control input, receiving input from a logic controller andinterrupting the relay control input signal when a current imbalance issensed, and enabling the fault indicator. In one presently preferredaspect of the method, interrupting of the circuit when a currentimbalance is sensed is maintained until the power source is cycled.Typically, the load being supplied with the current being monitored is amotor. In another preferred aspect, the current imbalance detection andcircuit interrupter requires no additional signals, inputs, wiring, orsources of power, but takes its power from the circuit being monitored.Alternatively, power may be drawn from an external source, such as anexternal relay control signal, for example. In one presently preferreduse of the method, the load side of the circuit is connected to a fuelpump, and arcing is terminated within the fuel pump.

In one presently preferred embodiment, the present invention isconfigured to perform ground fault detection and circuit interruption(GFI) and provides important advantages over prior art systems. Sincethe GFI system of the invention is packaged in the same envelope as anexisting relay system, it can be readily retrofit to existing aircraft.Since it is easily operated off of either AC or DC circuits, containingits own power supply powered by the circuit being monitored, it can beused on either AC or DC wired aircraft without further change orrewiring in the aircraft. Furthermore, since the GFI system of theinvention operates directly on and is part of the circuit beingmonitored, it avoids a major issue with prior art systems, which had tobe separately connected to the circuit being monitored. Anothersubstantial advantage to the present invention is that it more quicklyremoves power from the circuit with a fault, since sensing and controlis at a single location, thus providing in situ sensing and control.

The present invention also provides for an improved circuit protectiondevice for aircraft that can handle both carry-break andmake-carry-break types of ground fault conditions, and make-carry-breakfault current amplitudes, by providing the ground fault circuitinterrupter with relay contacts which are capable of survivingcarry-break and make-carry-break types of ground fault conditions at theanticipated current levels, and that comply with GFI requirements butstill maintain the size and configuration necessary for retrofitting toexisting aircraft and power controllers. In a preferred aspect, theelectronic and electromechanical elements of the current imbalancedetection and circuit interrupter are housed within a housing which hasa similar form factor to prior art power controllers. The inventionconnects with the circuit to be monitored and controlled, through theexisting power controller electrical connector, and it draws power fromthe circuit to be controlled. Alternatively, power may be drawn from anexternal source, such as an external relay control signal, for example.While there are numerous possible form factors, the most desirable formfactors are related to the power controllers used in aircraft. Thepresent invention also provides for an improved ground fault circuitinterrupter device that will perform a test at power up to confirm thatnone of the relay contacts have failed in a closed position, and tocheck that the switching FET which controls the relay coil has notshorted.

Other features and advantages of the present invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of a first embodiment of a controlsystem of the present invention adapted for a Boeing 757 aircraft, forinterrupting the circuit when a current imbalance is sensed.

FIG. 2 illustrates a detailed view of the power supply portion of thecontrol system shown in FIG. 1.

FIG. 3 illustrates a detailed view of the logic controller portion ofthe control system shown in FIG. 1.

FIG. 4 illustrates a detailed view of a sensor system for the controlsystem of FIG. 1.

FIG. 5 illustrates a block diagram of a second embodiment of a controlsystem of the present invention adapted for a Boeing 747 aircraft, forinterrupting the circuit when a current imbalance is sensed.

FIG. 6 illustrates a detailed view of the power supply portion of thecontrol system shown in FIG. 5.

FIG. 7 illustrates a detailed view of the logic controller portion ofthe control system shown in FIG. 5.

FIG. 8 illustrates a detailed view of a sensor system for the controlsystem of FIG. 5.

FIG. 9 illustrates a block diagram of an alternate preferred embodimentof a control system of the present invention adapted for providing thespeed of a DC relay in an AC application for interrupting the circuitwhen a current imbalance is sensed.

FIG. 10 illustrates a detailed view of a preferred embodiment of onesection of the power supply portion of the control system shown in FIG.9.

FIG. 11 illustrates a detailed view of a second section of the powersupply portion of the control system shown in FIG. 9.

FIG. 12 illustrates a detailed view of the preferred logic controllerportion of the control system shown in FIG. 9.

FIG. 13 illustrates a detailed view of a sensor system for the controlsystem of FIG. 9.

FIG. 14 is a side elevational view of an aircraft applicable currentimbalance detection and circuit interrupter according to the presentinvention.

FIG. 15 is a rear view of the aircraft applicable current imbalancedetection and circuit interrupter shown in FIG. 14.

FIG. 16 is a bottom view of the aircraft applicable current imbalancedetection and circuit interrupter shown in FIG. 14.

FIG. 17 is a side elevational partial cutaway view of the aircraftapplicable current imbalance detection and circuit interrupter shown inFIG. 14.

FIG. 18 is a sectional view of the aircraft applicable current imbalancedetection and circuit interrupter taken along line 18-18 of FIG. 17.

FIG. 19 is a sectional view of the aircraft applicable current imbalancedetection and circuit interrupter taken along line 19-19 of FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a preferred embodiment of a control system 10,adapted for a Boeing 757 aircraft, and FIG. 5 illustrates a preferredembodiment of a control system 10, adapted for a Boeing 747 aircraft,each being constructed in accordance with the present invention fordisconnecting power to a load when a current imbalance is sensed.Referring to FIGS. 1 and 5, the aircraft applicable current imbalancedetection and circuit interrupter 10 of the invention interrupts acircuit 20 having a line side 24 and a load side 26 with a ground fault.The load may be a motor, or any electrical device drawing a load, whereprotection of equipment or personnel is desired. The current imbalancedetection and circuit interrupter of the invention includes a powersupply 30, a sensor system 40, a logic controller 50, a power controller60, and a fault indicator and reset 55. In a preferred aspect, thesensor system may include a Hall effect device, a current transformer(CT), or a giant magneto resistive (GMR) device, for example, althoughother similar sensor devices may also be suitable. The power supply isconfigured to provide power to the logic controller, and the sensor isconfigured to sense a current imbalance in the line side 20 of thecircuit 24, and to output a sensor signal to the logic controller. Thelogic controller is configured to receive and process the sensor signalinput from the sensor and the relay control input signal, and the powercontroller is configured to receive input from the logic controller andremove power to the load side of the circuit when a current imbalance issensed.

FIGS. 2 and 6 illustrate a detailed view of a preferred embodiment ofthe power supply, and FIGS. 3 and 7 illustrate a detailed view of apreferred embodiment of the logic controller. Referring to FIGS. 4 and8, showing a sensor for use in the control system of the invention, in apreferred embodiment of the present invention, the sensor, which is anAmploc Pro 5 Hall effect linear current sensor with an output of 233mV/A when operated at 10V. All three line side wires pass through thesensor core. Kirchoff' s current law states that the net current in anode is 0. Considering the wye connection point of the load side pumpwinding, the net current in the phase windings, when algebraicallysummed, is 0. If a ground fault exists, that is where the current issupplied through the sensor but does not return through the sensor, thealgebraic sum of the currents in the phase wires would be equal to theground fault current.

Referring to FIGS. 3 and 7, in a preferred embodiment, the output of thesensor is approximately one-half of the supply voltage, for no measuredimbalance. Amplifier U3A amplifies the signal by a factor of 10. Thegain is set by the ratio of resistors R5 and R3. The 3 db point is wherethe reactance of capacitor C4 is equal to the resistance of R5. Thisoccurs at 3386 Hz. Resistors R1, R2, and R4 bias the amplifier and havebeen selected so that a maximum value of 1 meg, for resistor R4, isrequired to adjust the amplifier output to mid supply with the sensor atits specified worst case high output. Calibration for the worst case lowoutput of the sensor is easily achieved.

Amplifiers U3B and U3C, and resistors R6, R7, and R8 are set to detect acurrent imbalance of 3.0 Arms, for example, although other appropriatethresholds may also be suitable. A high output from amplifier U3B or U3Cindicates an imbalance is present in excess of the 3.0 Arms threshold,or other selected threshold. IC U4A “OR's” the outputs from amplifiersU3B and U3C. A logic 0 at its output indicates one or the other failurecondition is present. Simultaneous imbalance inputs can be handled butare physically not possible since a positive imbalance cannot exist atthe same time as a negative imbalance.

If a fault condition exists, it passes through IC U5A presenting a logic1 to the latch comprised of ICs U4B and U4C. A logic 1, at pin 5, forcesthe output pin 4 low, turning transistor Q1 off, which removes the drivesignal to the power relay control stage 17-1. Pin 9, the other input tothe latch, is normally at logic 0. This will cause pin 10 to go high,setting the latch by presenting a logic 1 to pin 6.

In a preferred embodiment, the power-up sequence initializes the powercontrol section to the non-operate mode. This is accomplished bypresenting a logic 0 to pin 2 of IC U5A to mimic a current imbalancecondition.

The power-up reset pulse created by IC U5B, resistor R13, capacitor C5and diode CR8 is typically 7 msec. The reset is determined by the timeit takes to charge capacitor C5 through resistor R13 to the thresholdset by IC U5B. Diode CR8 provides a quick reset.

At power-up, the GFI will perform a test to confirm that none of therelay contacts have failed closed, and to check that the switching FETwhich controls the relay coil has not shorted. These two failures arecritical items, which may prevent the GFI from interrupting a faultcurrent, and are therefore checked by the power-up built-in test (BIT).With the 3-phase 115 VAC power available at the time when the controlvoltage is switched ON, the status of the relay contacts is checked. Theinternal electronic circuits check to see if the contacts are all openjust before the relay is commanded closed, and also checks to see if allof the contacts are closed after the relay is commanded closed. If afault with the relay is detected, power to the relay coil is inhibited,and the mechanical fault indicator is activated. In another aspect, itmay also be advantageous to incorporate an auxiliary contact into therelay design, while still maintaining the GFI design within thepackaging constraints, in which case the status of the relay maincontacts for the 3-phase 115 VAC power could be checked by checking thestatus of the auxiliary contact.

Referring to FIGS. 2 and 6, diodes CR1, CR2, CR3, CR4, CR5, and CR6 forma full-wave three-phase bridge. Capacitor C1 acts as the storage devicefor the 281V peak voltage produced by the bridge. The regulator is apreferably buck-type configuration with the abnormal architecture ofhaving the inductor in the lower side. This is acceptable because thecircuit does not have to be referenced to earth ground. In fact, theon-board electrical ground is approximately 270 V above earth ground.

Preferably, the switcher operates in a non-conventional mode. If itsenses that output voltage is low, it turns on and remains on until thecurrent through inductor L1 reaches a pre-determined amount. Otherwise,the cycle is skipped. Energy is stored in inductor L1 and transferred tooutput capacitor C3 through diode CR7. Proper regulation is determinedby Zener VR1 and opto-coupler U2. Capacitor C2 serves to store a smallamount of energy that the regulator uses to operate its internalcircuitry.

Referring to FIGS. 9-13, illustrating an alternate preferred embodimentof a control system of the present invention adapted for an AC-DCapplication, to interrupt the circuit when a current imbalance issensed. As is shown in FIG. 9, the aircraft applicable current imbalancedetection and circuit interrupter 10 of the invention interrupts acircuit 20 having a line side 24 and a load side 26 with a ground fault.The load may be a motor, or any electrical device drawing a load, whereprotection of equipment or personnel is desired. The current imbalancedetection and circuit interrupter of the invention includes a powersupply 30, a sensor system 40, a logic controller 50, a power controller60, and a fault indication and reset 55. In a preferred aspect, thesensor system may include a Hall effect device, a current transformer(CT), or a giant magneto resistive (GMR) device, for example, althoughother similar sensor devices may also be suitable. The power controllercan be controlled by direct current (DC), or alternatively may becontrolled by alternating current (AC). The power supply is configuredto provide power to the logic controller, and the sensor is configuredto sense a current imbalance in the line side 20 of the circuit 24, andto output a sensor signal to the logic controller. The logic controlleris configured to receive the relay control input signal and to receiveand process the sensor signal input from the sensor, and the powercontroller is configured to receive input from the logic controller andremove power to the load side of the circuit when a current imbalance issensed.

FIGS. 10 and 11 illustrate a detailed view of a preferred embodiment ofthe power supply. FIG. 12 illustrates a detailed view of a preferredembodiment of the logic controller. Referring to FIG. 13, showing asensor for use in the control system of the invention, in a preferredembodiment of the present invention, the sensor, which is an Amploc Pro5 Hall effect linear sensor with an output of 233 mV/A when operated at10V. All three line side wires pass through the sensor core. Kirchoff' scurrent law states that the net current in a node is 0. Considering thewye connection point of the load side pump winding, the net current inthe phase windings, when algebraically summed, is 0. If a ground faultexists, that is where the current is supplied through the sensor butdoes not return through the sensor, the algebraic sum of the currents inthe phase wires would be equal to the ground fault current.

Referring to FIGS. 12, in a preferred embodiment, the output of thesensor is approximately one-half of the supply voltage, for no measuredimbalance. Amplifier U3A amplifies the signal by a factor of 10. Thegain is set by the ratio of resistors R5 and R3. The 3 db point is wherethe reactance of capacitor C4 is equal to the resistance of R5. Thisoccurs at 3386 Hz. Resistors R1, R2, and R4 bias the amplifier and havebeen selected so that a maximum value of 1 meg, for resistor R4, isrequired to adjust the amplifier output to mid supply with the sensor atits specified worse case high output. Calibration for the worse case lowoutput of the sensor is easily achieved.

Amplifiers U3B and U3C, and resistors R6, R7, and R8 are set to detect acurrent imbalance of 3.0 Arms, for example, although other appropriatethresholds may also be suitable. A high output from amplifier U3B or U3Cindicates an imbalance is present in excess of the 3.0 Arms threshold,or other selected threshold. IC U4A “OR's” the outputs from amplifiersU3B and U3C. A logic 0 at its output indicates one or the other failurecondition is present. Simultaneous imbalance inputs can be handled butare physically not possible since a positive imbalance cannot exist atthe same time as a negative imbalance.

If a fault condition exists, it passes through IC U5A presenting a logic1 to the latch comprised of ICs U4B and U4C. A logic 1, at pin 5, forcesthe output pin 4 low, turning transistor Q1 off, which removes the drivesignal to the power control stage. Pin 9, the other input to the latch,is normally at logic 0. This will cause pin 10 to go high, setting thelatch by presenting a logic 1 to pin 6.

In a preferred embodiment, the power-up sequence initializes the powercontrol section to the non-operate mode. This is accomplished bypresenting a logic 0 to pin 2 of IC U5A to mimic a current imbalancecondition.

The power-up reset pulse created by IC U5B, resistor R13, capacitor C5and diode CR8 is typically 7 msec. The reset is determined by the timeit takes to charge capacitor C5 through resistor R13 to the thresholdset by IC U5B. Diode CR8 provides a quick reset.

At power-up, the GFI will perform a test to confirm that none of therelay contacts have failed closed, and to check that the switching FETwhich controls the relay coil has not shorted. These two failures arecritical items, which may prevent the GFI from interrupting a faultcurrent, and are therefore checked by the power-up built-in test (BIT).With the 3-phase 115 VAC power available at the time when the controlvoltage is switched ON, the status of the relay contacts is checked. Theinternal electronic circuits check to see if the contacts are all openjust before the relay is commanded closed, and also checks to see if allof the contacts are closed after the relay is commanded closed. If afault with the relay is detected, power to the relay coil is inhibited,and the mechanical fault indicator is activated. In another aspect, itmay also be advantageous to incorporate an auxiliary contact into therelay design, while still maintaining the GFI design within thepackaging constraints, in which case the status of the relay maincontacts for the 3-phase 115 VAC power could be checked by checking thestatus of the auxiliary contact.

Referring to FIGS. 10 and 11, diodes CR1, CR2, CR3, CR4, CR5, and CR6form a full-wave three-phase bridge. Capacitor C1 acts as the storagedevice for the 281V peak voltage produced by the bridge. The regulatorsare a buck-type configuration with the abnormal architecture of havingthe inductor in the lower side. This is acceptable because the circuitdoes not have to be referenced to earth ground. In fact, the on-boardelectrical ground is approximately 270V and 260V above earth ground forthe 10 V and 20V supplies respectively.

Preferably, the switcher operates in a non-conventional mode. If it issensed that an output voltage is low, the corresponding controller turnson and remains on until the current through inductor L1 or L1A reaches apre-determined amount. Otherwise, the cycle is skipped. Energy is storedin inductor L1 or L1A and transferred to output capacitor C3 or C3Athrough diode CR7 or CR7A. Proper regulation is determined by Zener VR1or VR1A and opto-coupler U2 or U2A. Capacitor C2 or C2A serves to storea small amount of energy that each respective regulator uses to operateits internal circuitry.

Most aircraft presently in service utilize circuit breakers with thelimitations previously discussed. While the electronic andelectromechanical aspects of the present invention impart additionalprotection to the protection provided by such circuit breakers, it wouldbe desirable to be able to package the invention in a form which wouldallow ease of retrofit to existing aircraft, newly constructed and newaircraft designs, thus bringing the benefits of the invention to a widerrange of applications. Accordingly, in a further presently preferredaspect of the invention, the electronic and electromechanical elementsof the current imbalance detection and circuit interrupter are housedwithin a housing which has a similar form factor to prior art powercontrollers. The invention connects with the circuit to be monitored andcontrolled through the existing power controller electrical connector,and it draws power from the circuit to be controlled. Alternatively,power may be drawn from an external source, such as an external relaycontrol signal, for example. While there are numerous form factors whichcan impart additional protection to the protection provided by suchcircuit breakers, one of our form factors is related to the powercontrollers used in the Boeing 757 aircraft and the like, which have aninstalled height of approximately 1.78 inches above the mountingsurface, a width of approximately 1.53 inches above the mountingsurface, and a total height of 3.28 inches from the top to the bottom ofthe electrical terminals.

With reference to FIG. 14, in one presently preferred aspect of theinvention, each of the above described circuit configurations can beadvantageously contained in a corresponding housing 70, which istypically no more than about 3.28 inches (about 8.33 cm.) from top 72 tobottom 74, no more than about 1.53 inches (about 3.89 cm.) wide alongits front 76 and rear 78 sides, and no more than about 2.51 inches(about 6.38 cm.) from the front side 80 of the front mounting flange 82to the rear side 84 of the rear mounting flange 86. The housing alsoincludes a relay 87, typically a one-inch cube relay, having contactsrated for a 25 Amp GFI to make-carry-break fault current levels of about500 Amps, and 15 or more ground fault cycles with no appreciable changein contact resistance, or a relay rated for a 50 Amp GFI tomake-carry-break fault current levels of about 1500 Amps, and 15 or moreground fault cycles with no appreciable change in contact resistance.

Referring to FIG. 14, FIG. 15, and FIG. 16, an electrical connectormeans such as the terminal block or connector plate 88 is provided atthe bottom of the aircraft applicable current imbalance detection andcircuit interrupter housing, typically with eight screw-type electricalconnectors, A1, A2, X1, B1, B2, C1, C2, and X2, although otherconventional types of wire connectors may also be suitable. Referring toFIG. 4, FIG. 8, FIG. 13 and FIG. 16, the connectors A1 and A2accommodate a first line and load A; the connectors B1 and B2accommodate a second line and load B, and the connectors C1 and C2 willaccommodate a third line and load C. As is shown in FIG. 15 and FIG. 16,the connector plate is mounted to the housing of the aircraft applicablecurrent imbalance detection and circuit interrupter by mounting screws90, which extend through sleeves 92 in the housing, illustrated in FIG.18 and FIG. 19, as is explained further below.

Referring to FIG. 17, FIG. 18 and FIG. 19, one or more circuit boards,such as a first printed circuit board 94 and a second printed circuitboard 96, for mounting the components of the above described circuitconfigurations, can be mounted within the housing with notches 98 in theprinted circuit boards fitting around the sleeves 92 of the mountingscrews 90.

It should be appreciated that while the logic controller has beendisclosed as being implemented as an electronic circuit, the logiccontroller may also be implemented as a microprocessor based logiccontroller, and other components of the aircraft applicable currentimbalance detection and circuit interrupter of the invention may also beimplemented at least in part by one or more microprocessors.

From the above, it may be seen that the present invention provides amethod and apparatus for suppressing arcs in electrical equipment inaircraft which may be adapted to a variety of systems and components. Assuch, it provides additional reliable and rapid disconnect of power tothe existing systems, thus reducing damage from ground faults in thecircuits. While a particular form of the invention has been illustratedand described it will also be apparent that various modifications can bemade without departing from the spirit and scope of the invention.Accordingly, it is not intended that the invention be limited except asby the appended claims.

1-35. (canceled)
 36. An aircraft applicable current imbalance detectionand circuit interrupter device for retrofitting a circuit breaker in anexisting application wherein such circuit breaker complies with a formfactor, engages a connector to interface with a line side and a loadside of an electrical circuit and controls a current path from said lineside to said load side, comprising: a housing complying with said formfactor and including a connection means for engaging said connector; asensor system disposed in the housing for sensing a current imbalance inthe electrical circuit and for providing a sensor signal indicating theexistence of an undesirable current within the electrical circuit basedon said sensing of said current imbalance; a logic controller disposedin the housing and configured to receive the sensor signal from thesensor system and to output a fault signal representing a fault; and apower controller disposed in the housing configured to receive saidfault signal from the logic controller and to remove power to the loadside of the electrical circuit responsive to the fault signal from thelogic controller, the power controller including a power relay havingcontacts capable of surviving carry-break and make-carry-break types ofground fault conditions at anticipated current levels.
 37. The aircraftapplicable current imbalance detection and circuit interrupter device ofclaim 36, wherein the aircraft applicable current imbalance detectionand circuit interrupter interrupts arcing within a device being operatedby the electrical circuit.
 38. The aircraft applicable current imbalancedetection and circuit interrupter device of claim 36, wherein thehousing has an envelope compatible with that of existing powercontrollers for the aircraft and using the same monitoringconfigurations.
 39. The aircraft applicable current imbalance detectionand circuit interrupter device of claim 36, wherein the electricalconnector means comprises an electrical connector plate on the housingconnected to the line side and load side of the electrical circuit beingmonitored.
 40. The aircraft applicable current imbalance detection andcircuit interrupter device of claim 39, wherein said electricalconnector plate comprises a plurality of electrical connectors.
 41. Theaircraft applicable current imbalance detection and circuit interrupterdevice of claim 40, wherein said electrical connector plate comprises afirst pair of connectors accommodating a first load line, a second pairof connectors accommodating a second load line, and a third pair ofconnectors accommodating a third load line.
 42. The aircraft applicablecurrent imbalance detection and circuit interrupter device of claim 36,wherein the aircraft applicable current imbalance detection and circuitinterrupter is configured to test during a power up sequence todetermine if the aircraft applicable current imbalance detection andcircuit interrupter is operating properly.
 43. An aircraft applicablecurrent imbalance detection and circuit interrupter device forretrofitting a circuit breaker in an existing application, wherein suchcircuit breaker complies with a form factor, engages a connector tointerface with a line side and a load side of an electrical circuit andcontrols a current path from said line side to said load side,comprising: a housing complying with said form factor and includingconnection means for engaging said connector; a sensor system disposedin the housing for sensing a current imbalance in the electrical circuitand for providing a sensor signal indicating the existence of a currentimbalance within the electrical circuit based on said sensing of saidcurrent imbalance; a logic controller disposed in the housing andconfigured to receive an external relay control signal and the sensorsignal from the sensor system, and to compare the sensor signal with apredetermined range for acceptable operation for the electrical circuitand to interrupt the relay control signal when the sensor signal exceedssaid predetermined range; a power controller configured to be energizedby the relay control signal and to remove power to the load side of theelectrical circuit when the relay control signal is interrupted, thepower controller including a power relay having contacts capable ofsurviving carry-break and make-carry-break types of ground faultconditions at anticipated current levels; a fault indicator configuredto receive said fault signal from the logic controller, to illuminateindicating a current imbalance condition has occurred; and a resetswitch to reset the fault indicator and the current imbalance detectionand circuit interrupter.
 44. The aircraft applicable current imbalancedetection and circuit interrupter device of claim 43 wherein: the logiccontroller receives the relay control signal to directly power the powercontroller; the relay control signal, depending on the aircraft, may bealternate current (AC) or direct current (DC); and the type of powercontroller corresponds to the AC or DC relay control signal.
 45. Theaircraft applicable current imbalance detection and circuit interrupterdevice of claim 43, wherein the aircraft applicable current imbalancedetection and circuit interrupter receives power to operate exclusivelyfrom the line side of the electrical circuit being monitored.